LegendItem
A legend item, which often represents a sub-class of features in a
layer in the case of categorical or classed layers.
title: string | string[]
The title of the legend item.
titleDependsOnZoom
titleDependsOnZoom: boolean
Whether the title depends on the zoom level or not. If it does, you
need to call when the zoom level changes.
Note that as the zoom level changes, the handler
will not be called, so you need to call yourself.
visible: boolean
Whether the legend item is visible or not.
id: string
The id of the legend item.
layerId: string
The id of the layer the legend item belongs to.